What are horns,nails,and hair made of?

Polypeptide chains present in insulin are linked together by:

Which protein is present in the exoskeleton?

Statement $P$: The quaternary structure of proteins is either globular or fibrous.
Statement $Q$: The three-dimensional arrangement of molecules consisting of a single polypeptide chain is the quaternary structure of proteins.

Assertion : The amino acid glycine comes under the category of nonessential amino acids.
Reason : This is due to the fact that it can not be synthesised in the body.

Insulin is